1. Field of the Invention
The invention relates to the field of wafer fabrication photolithography equipment and, more specifically, to cross-masks for stepper machines.
2. Prior Art
In the field of stepper machines for semiconductor wafer fabrication it is necessary to have cross-masks or some other method for aligning wafers in the stepper machines. By examining wafer alignment through a cross-mask device, wafers may be aligned in a stepper machine for subsequent processing. Proper alignment of the wafers in stepper machines is extremely important and becomes increasingly important as die size decreases and processing parameters are tightened.
One known cross-mask and holder device comprises a holder with screws for adjusting a separate cross-mask plate. This device suffers from requiring an extemely long set-up time for adjusting the cross-mask, due to movement of the cross-mask plate while tightening the screws. In addition, adjustment of the cross-mask is only possible in the x and the y direction and not in a Theta direction. This prior art cross-mask and holder device will be described in more detail in conjunction with FIG. 1(a).
Another known device comprises a cross-mask holder with the cross-mask permanently attached to the holder. This method allows movement of the cross-mask in only one direction, although it does offer an advantage of protecting the cross-mask from damage. In addition, this method utilizes an adjustment device which reduces the amount of time required for adjusting the cross-mask. However, the accuracy of the adjustment is less than that desired. This cross-mask will be more fully described in conjunction with FIG. 1(b).